This invention relates to novel optically active compounds and chiral liquid crystal compositions incorporating such novel optically active compounds.
Liquid crystal displays have advantages in that they are actuated by a low electric voltage, that they consume only a little electric power, that they are fabricated into thin layer forms, and that they are relatively light in weight. Making use of these advantages, liquid crystal display devices are applied for use in desk electric calculators, watches and televisions. Nematic liquid crystals have hitherto been widely used as the materials for such display elements. However, nematic liquid crystals are detrimental in that the response speeds thereof are low, i.e. in the order of several tens milliseconds. In order to avoid the disadvantage of the nematic liquid crystals, it has been proposed to use ferroelectric liquid crystals in the display system, for example, by N. A. Clark et al., "Submicrosecond Bistable Electro-Optic Switching in Liquid Crystals", Appl. Phys. Lett., 36, 899 (1980). In the display system proposed by this prior art reference, the chiral smectic C liquid-crystalline phase (hereinafter referred to as "Sc' phase") of a ferroelectric liquid crystal is utilized. However, the known ferroelectric liquid crystal compounds are detrimental in that they exhibit the Sc' phase in only a narrow temperature range and that the spontaneous polarization thereof is low.
In order to apply ferroelectric liquid crystals in a practical electro-optic switching element, it has been tried to use a mixture containing a compound having high spontaneous polarization or inducing high spontaneous polarization, a compound having a low viscosity, compounds having reverse helical twists, and compounds which exhibit the Sc or Sc' phase in a wide temperature range. But no satisfactory results were obtained.